The present invention relates to a method for manufacturing a motorcycle tire provided in the tread portion with a breaker and a band, more particularly to a method for building a raw tire by the use of breaker support rings capable of improving the uniformity of the tire.
In a method for manufacturing a pneumatic tire for four-wheeled vehicles, a widely employed process for building a raw tire is as follows.
As shown in FIG. 11, a carcass ply c1 is wound into a cylindrical shape on a carcass building drum (not shown) and bead cores c2 are fitted on the cylindrical carcass c to form a cylindrical raw tire main body d. On the other hand, breaker plies b1, a band ply b2 and a tread rubber b3 are wound on a tread building drum (not shown) to form a cylindrical tread assembly b separately from the raw tire main body d. Then, by the use of a shaping drum e, the cylindrical raw tire main body d is swollen or shaped into a toroidal form by the use of an inflatable bladder for pressurizing the inside of the raw tire so that the crown portion of the swollen raw tire main body d adheres to the tread assembly b waiting on the radially outside of the raw tire main body d. Further, both edge portions of the cylindrical tread assembly b are turned down onto the toroidal raw tire main body d by the use of pressure rollers fl so that the entirety of the tread assembly b adheres to the raw tire main body d.
In a motorcycle tire whose tread portion has a relatively small radius of curvature when compared with the passenger car tires, truck/bus tires and the like, the radius of curvature of the crown portion of the toroidal raw tire main body d is also relatively small. Therefore, if the above-mentioned manufacturing method is employed, when the edge portions of the cylindrical tread assembly are turned down onto the toroidal raw tire main body, the breaker cord arrangement and the band cord arrangement are liable to be disturbed. In particular, since the band cord angle with respect to the tire circumferential direction is small, the band is liable to cause undulation when pressed. Thus, the band is liable to exert a bad influence on the tire uniformity than the breaker whose cord angles are relatively small and cord lengths are relatively short.
Thus, it is difficult to improve the uniformity of a motorcycle tire provided with a breaker and a band.